A radar unit can emit electromagnetic waves bundled into a primary signal, and receive the signals reflected from an object, and evaluate these according to manifold requirements and fields of application. In this manner, data regarding the object can be obtained, for example, a distance to the object, a relative movement between the transmitter (radar unit) and the object, as well as the shape of the object. Radar units are used in air traffic control, as weather radar, for research purposes in astronomy, for tracking targets in air defense, for monitoring buildings, and in a motor vehicle for monitoring the vehicle environment, to name just a few examples. Radar units can be designed as mobile and stationary radar units.
The requirements for the radar units that can be used in the vehicle assistance system of the motor vehicle are manifold, in particular, the radar unit must be able to be integrated in the motor vehicle without difficulties. For this, sensors for the radar unit are preferably disposed in the region of the motor vehicle bumper, behind the respective bumper, for example. The monitoring of the vehicle environment requires of the radar unit that an object must be able to be detected at an early stage, by means of which a special requirement is defined for the range of the radar unit that is implemented. Furthermore, a satisfactory distinction of objects is necessary, resulting in a high demand on the distance resolution being required, in particular in close range.
The range of a radar unit is determined by the mean transmission output. Deviations in the transmission output and/or a drift in the transmission output that has been set can lead to an imprecise determination of the distance, and should be avoided. For this reason, it is important in the operation of the radar unit that the transmission output be monitored and that it be possible to detect defects in the hardware of the radar unit in a timely manner.
A radar unit is known from DE 10 2011 055 693 A1, having a transmission path and a receiving path with two receiving channels and a control means, and is configured for detecting a channel malfunction in the receiving channel. For this, the input of an oscillator in the transmission path is connected to the control means, and the oscillator can be activated by the control means in order to generate a signal. The receiving channel is configured for receiving the signal returning from the object. The channel malfunction can be detected in that the control means is configured to activate the oscillator for generating a first signal component, which contains signal components, the frequencies of which exhibit a lower cutoff frequency for the frequency band, and an upper cutoff frequency for the frequency band, wherein the signal fragments with the lower cutoff frequency and the signal fragments with the upper cutoff frequency can be generated in an alternating manner.